Clearview National March 2018 - Issue 196 - Page 68

GLASS&SEALEDUNITS
CHOOSING
THE BEST
GLASS
TYPE FOR
OVERHEAD
GLAZING
» » WITH THE MYRIAD OF GLASS TYPES
available now, it is often confusing what to
choose in terms of safety, thermal and solar
performance and balancing cost with the
benefits on offer. Richard Burgess, Managing
Director of patent glazing and roof light
manufacturer Lonsdale Metal Company Ltd
shares his experience of thirty years in the
industry.
SAFETY
Above all, safety is the critical factor
in overhead glazing and the table below
summarises what type of glass complies
with current Building Regulations at time of
writing:
From time to time, it is desirable to use
Wired Glass in double glazed combinations.
However, there is a high risk of breakage due to
thermal stress and advice should be sort from
the sealed unit manufacturer.
It is not recommended to use toughened
glass in single glazing or to the inner pane of
double glazed units over swimming pools,
food & beverage preparation units or any areas
where the small broken pieces characteristic to
this glass type, could cause subsequent injury
due to contamination. In these situations
laminated glass or polycarbonate would be the
best choices.
68 » M AR 2018 » CL EARVI E W- UK . C O M
DOUBLE GLAZING
More or less without exception, the outer pane
of a double glazed unit should be toughened
glass. The inner pane may be toughened or
laminated depending upon location and
height above ground. Generally two sheets of
toughened glass provide the most economical
solution for domestic projects where the roof
light is no more than 5m above floor level. If the
height exceeds this, then laminated glass should
be used for the inner pane.
WHEN IT COMES TO
PERFORMANCE, THE FOLLOWING
ARE FEATURES TO CONSIDER:
Low-e coating – offers improved thermal
efficiency retaining more heat within the
building.
There are to type available standard ‘hard’
coat finish or the more popular ‘soft’ coat which
offers a typical centre pane uvalue of 1.2W/m2
when combined with an argon filled cavity.
Tinted anti-sun glass – body tinted
toughened glass can be used as the outer pane
combined with a laminated low-e softcoat glass
to give the added benefit of reducing solar heat
gain in the summer months at reasonable cost.
This is most commonly used in blue, but green,
grey and bronze colours are also available.
Typically this provides a 50% reduction in solar
transfer and 50% light transmission.
Neutral solar control glass – has a special
coating that provided improved solar control
and appear more neutral in colour albeit with
a slight grey/green tint. This is often described
as 70/30 meaning it offers a 70% light
transmission, but only 30% of the sun’s heat
enters the building.
TRIPLE GLAZING
All of the above glass type can be combined
in a triple glazed units achieving both
improved sound insulation and U-values as
low as 0.60W/m2.K Consideration however,
must be given to the additional weight and
handling during installation.
LARGE PANE ROOFLIGHTS
The most economic glass tends to be
4-6mm thick which rarely can be installed
wider than 1000mm, hence most domestic
roof lantern and conservatory installation
featuring glazing bars every 600 to 900mm.
However, with the current trend for flat
rooflights, single pane rooflights can be
installed up to 3m x 6m in one pane of
glass. This calls for specialist manufacturing
and installation by experienced companies
with the necessary handling equipment
and expertise. Much thicker toughened &
laminated glass is required so as not to deflect
and care must be taken to ensure compliance
with building regulations and local, design
wind & snow loads.
www.lonsdalemetal.co.uk